An LED is a light-emitting device formed by carrying an electroluminescent semiconductor module on a substrate (a reflector) and encapsulating with epoxy resin or silica gel and the like. The LED has various extremely excellent characteristics, such as small volume and light weight, so as to be applied for a variety of lighting equipments. In addition, the service life can be up to 100,000 hours; the color is vivid and conspicuous, showing excellent visual performance and low power consumption. To obtain the advantages above-mentioned, the reflector not only can be expected to be shaped precisely, but also has good heat resistance. Stable and high reflectivity is especially indispensable for the performance of reflected light, and that yellowing and reflectivity reducing due to heating of the LED reflector must be negligible after assembling and soldering processes. In prior art, for example, Chinese patent CN02826032.5 discloses a resin composition for a reflecting plate, which is formed by adding potassium carbonate fiber or wollastonite into an aromatic polyamide resin and adding TiO2 if necessary. The resin composition has good heat resistance and dimension stability to some extent, but with the disadvantages of insufficient long-term thermal aging resistance and obviously reduced reflectivity. U.S. Patent US 2008167404A1 discloses an aromatic polyamide composition and articles manufactured therefrom, wherein the aromatic polyamide composition comprises more than 5 wt % of at least one crystalline silicate, more than 2 wt % of at least one white pigment, and more than 1 wt % of at least one optionally functionalized olefin copolymer and aromatic polyamide, leading to the polyamide compositions with insufficient initial whiteness and reflectivity. Chinese patent CN 200680011812.X discloses a resin composition for a reflecting plate and a reflecting plate itself, wherein the resin composition for the reflecting plate comprises 30-80 wt % of polyamide, 10-60 wt % of an inorganic filler and 5-50 wt % of a white pigment. The resin composition presents itself as a combination of good mechanical strength and high reflectivity. But the molding shrinkage and linear expansivity are large; therefore, the dimensional stability is poor. World patent WO 03/085029 discloses a polyamide resin for an LED reflector by adopting 1,9-diaminononane as diamine component. However, the polyamide resin fails to avoid reducing the reflectivity sufficiently due to heating during assembling and soldering processes of the LED